This invention relates to a new catalyst composition useful for initiating and promoting polymerization of one or more .alpha.-olefins and to a polymerization process employing such a catalyst composition.
It is well known that olefins such as ethylene, propylene, and 1-butene in the presence of metallic catalysts, particularly the reaction products of organometallic compounds and transition metal compounds can be polymerized to form substantially linear polymers of relatively high molecular weight. Typically such polymerizations are carried out at relatively low temperatures and pressures.
Among the methods for producing such linear olefin polymers, some of the most widely utilized are those described by Professor Karl Ziegler in U.S. Pat. Nos. 3,113,115 and 3,257,332. In these methods, the catalyst employed is obtained by admixing a compound of a transition metal of Groups 4b, 5b, 6b and 8 of Mendeleev's Periodic Table of Elements with an organometallic compound. Generally the halides, oxyhalides and alkoxides or esters of titanium, vanadium and zirconium are the most widely used transition metal compounds. Common examples of the organometallic compounds include the hydrides, alkyls and haloalkyls of aluminum, alkylaluminum halides, Grignard reagents, alkali metal aluminum hydrides, alkali metal borohydrides, alkali metal hydrides, alkaline earth metal hydrides and the like. Usually, the polymerization is carried out in a reaction medium comprising an inert organic liquid, e.g., an aliphatic hydrocarbon and the aforementioned catalyst. One or more olefins may be brought into contact with the reaction medium in any suitable manner, and a molecular weight regulator, such as hydrogen, is often added to the reaction vessel in order to control the molecular weight of the polymers. Such polymerization processes are either carried out at slurry polymerization temperatures (i.e., wherein the resulting polymer is not dissolved in the hydrocarbon reaction medium) or at solution polymerization temperatures (i.e., wherein the temperature is high enough to solubilize the polymer in the reaction medium).
Following polymerization, it is common to remove catalyst residues from the polymer by repeatedly treating the polymer with alcohol or other deactivating agent such as an aqueous basic solution. Such catalyst deactivation and/or removal procedures are expensive both in time and material consumed as well as the equipment required to carry out such treatment.
Gessell's U.S. Pat. No. 4,244,838 and 4,246,383 and pending applications Ser. No. 192,959 filed Oct. 1, 1980 and now U.S. Pat. Nos. 4,496,660, and 192,960 filed Oct. 1, 1980 and now abandoned, by Gessell, Gibbs and Fuentes, Jr., disclose catalysts prepared by employing an organic hydroxyl-containing material. However, such catalysts are directed only to the resultant solid reaction product which must be separated from the liquid portion and washed. It would be desirable to employ a catalyst which does not require the recovery of the solid reaction product and the attendant washing steps.
It is advantageous for ethylene polymers to have a broad molecular weight distribution for the purpose of producing bottles, pipes, films, and coatings by blow molding, since polymers having a narrow molecular weight distribution have poor melt flowability and are harder to process than broad molecular weight distribution polymers. Also narrow molecular weight distribution polymers require more energy to process them by extrusion methods and give products that have rough surfaces due to melt fracture of the polymer. The rough surface is an undesirable property and leads to lower commercial value of the product.
The present invention provides a catalyst for polymerizing .alpha.-olefins which catalysts are sufficiently efficient so as to not require their removal from the polymer and their preparation does not require recovery and washing of the solid reaction product. The present invention also produces polymers having a relatively broad molecular weight distribution.